In the field of machining a crankshaft which is commonly used as a part of an engine and so forth, it has hitherto been known to machine a pin journal or a main journal of the crankshaft by using a crankshaft miller that is typically unavailable to machine the outer periphery of a counter weight and the other components of the crankshaft. Then, since the outer periphery of the counter weight and so forth have to be machined separately by means of a machine tool such as a lathe, it has hitherto been a common recognition that a multiple number of process steps are required in machining a crankshaft, thus rendering its productivity significantly low.
In order to overcome such an inconvenience, Japanese Unexamined Patent Publication No. Hei 6-320319 has proposed a crankshaft miller arrangement which enables the periphery of a counter weight in a crankshaft to be machined with a cutter for machining a main journal of the crankshaft.
The crankshaft miller system disclosed in the above mentioned publication is constituted of a bed, a pair of work heads which are mounted on the bed and adapted to support one end and the other of a workpiece to be machined, respectively, and a pair of cutter units disposed between these work heads so as to be movable in the longitudinal direction of the workpiece. One of these cutter units is provided with a cutter for machining a pin journal as well as a rest unit operative, when the pin journal is machined with the cutter, to clamp a main journal adjacent to the pin journal, and the other cutter unit is provided with a cutter for machining the main journal as well as a rest unit for clamping a main journal adjacent to one of a pair of counter weights the other of which can be machined with the main journal machining cutter. This arrangement, with the ability to machine the outer periphery of such a counter weight with the main journal machining cutter, has been recognized to be effective to reduce the number of machining process steps as compared with a case where it can be machined only in a separate process step by using a lathe or the like, hence enhancing the productivity to prepare a machined crankshaft.
Because of the need to machine the outer periphery of a counter weight one by one with the main journal machining cutter, it has been found, however, that the crankshaft miller system disclosed in the above mentioned publication makes it necessary for a prolonged time period to be expended in machining a single crankshaft, thus giving rise to the inconvenience of a reduced machining efficiency.
With the view to eliminating such inconveniences as encountered in the prior art, it is an object of the present invention to provide a crankshaft machining apparatus that makes it possible for a pair of counter weights of a given crankshaft to be simultaneously machined in their respective outer peripheries, thereby enhancing the efficiency of the process of machining a crankshaft.